To oxidize sulfide sulfur and thereby permit solubilization of metals compounded with the sulfide sulfur, base metal ores and concentrates, and refractory gold ores and Concentrates are commonly treated by pressure oxidation. Pressure oxidation is typically performed by passing a feed slurry of a metal-containing material through a sealed autoclave (operating at superatmospheric pressure) having multiple compartments. To provide for oxidation of the sulfide sulfur in the slurry, oxygen is typically fed continuously to the autoclave by means of a sparge tube located below the impeller. Commonly a large portion of the oxygen reacts with the sulfide sulfur, but there is a smaller significant portion that is vented from the autoclave and may be considered not effectively utilized.
In designing an autoclave, there are a number of considerations. By way of example, the autoclave should permit reaction of as much of the oxygen as possible with sulfide sulfur. If the oxygen is inefficiently reacted with the sulfide sulfur, the autoclave can have higher oxygen plant capital and operating costs. The autoclave should provide as short a residence time as possible for a given volume of slurry while realizing a high rate of recovery for the metal. Finally, the autoclave should vent inert gases that build up in the autoclave above the slurry to prevent rupturing of the autoclave from high pressure gas. Some oxygen gas is inevitably vented along with these inert gases. Other processes, which rely on efficient and effective gas/liquid transfer of oxygen and which are commonly carried out in autoclaves, include catalytic chemistry reactions, such as the conversion of ferrous to ferric ions, reoxidation of NO by oxygen, and cuprous amine conversion to cupric amine.